While the production of polyolefin-based fiber, webs and corresponding nonwoven materials is well known in the textile art, attempts to broadly apply such general knowledge to produce products for personal hygiene purposes, such as catamenial devices, disposable diapers, incontinence pads and the-like, have met with serious technical problems due to significant differences in required fiber-spinning and working characteristics as opposed to properties desired in the final products.
In general, such products must have a fluid-absorbent core, usually comprising one or more layers of absorbent material such as wood pulp, rayon, gauze, tissue and the like and, in some cases, synthetic hydrophilic materials identified as super-absorbent powders such as a polyacrylate salt.
Such a fluid-absorbing core is most generally-shaped in the form of a pad of wood pulp, fiber and conjugate fiber, arranged in a rectangular or somewhat oval shape. To protect the wearer's clothing, and surrounding areas from stain or wetting by fluids already absorbed in such core, an externally positioned fluid-impervious barrier sheet is usually required. In addition, the absorbent device is separated from the body of the user by a one way water-permeable nonwoven cover sheet or facing contacting the body.
A particularly troublesome technical problem arises where a high degree of hydrophobicity is desired in a nonwoven coversheet component consisting substantially of conventionally bonded webs of hydrophobic fiber such as polyolefin-containing staple fiber.
In general, untreated hydrophobic fiber of such type quickly becomes unworkable due to friction and accumulated static charges during conventional spinning, crimping, cutting and carding operations. For this reason, the prior art has lone-recognized and used a variety of topically applied lubricant and antistatic agents which impart hydrophilic properties to an extent sufficient to permit conventional fiber processing. In commercial use, however, such treatment frequently results in a final fiber or nonwoven product which is substantially more hydrophilic than desired.
In particular, because of the nature of commercial high speed operations, and the somewhat unpredictable affinity of known lubricating and antistatic agents to individual fiber batches of the hydrophobic-type, it is very difficult to maintain adequate control over the wetting characteristics of the final nonwoven product.
It is an object of the present invention to prepare hydrophobic polyolefin-containing spun fiber or filament for conventional fiber processing, inclusive of crimping, cutting, carding and bonding steps, without sacrificing hydrophobic characteristics of the commercial product.